Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: L_Roy_Saint on April 04, 2012, 10:49:15 am

Title: SVT-CL volume fluctuates while using -15dB input.
Post by: L_Roy_Saint on April 04, 2012, 10:49:15 am

SVT-CL volume fluctuates while using -15dB input.  All tubes test ok.  Volume will either start at a lower volume and sudedenly jump after 20-30 minutes use or start high and drop by about half.  This repeats itself.  Sound familiar?

Title: Re: SVT-CL volume fluctuates while using -15dB input.
Post by: PRR on April 06, 2012, 12:38:02 am

> while using -15dB input.

Dirty jack, bad solder joints on jack and resistors, bad resistors.

Title: Re: SVT-CL volume fluctuates while using -15dB input.
Post by: L_Roy_Saint on April 06, 2012, 05:58:52 am

Thank you.  I will check it out.

Title: Re: SVT-CL volume fluctuates while using -15dB input.
Post by: L_Roy_Saint on April 25, 2012, 06:30:26 am

SUCCESS!
The problem was the 0db input jack.  The two leads which make contact when the jack is vacant weren't making proper contact, causing the preamp to operate in unbuffered mode.  I cleaned the contacts thoroughly with alcohol and verified their continuity with a DMM.
While I had the preamp out of the unit I noticed alot of flux on the bottom of the pcb.  I cleaned this as well.